In a solid-state image pickup device used in a digital camera, it is generally difficult to widen the dynamic range of image because electric charges corresponding to image signals are detected by photoelectric conversion elements (hereinafter also referred to as “pixels”). Therefore, use of a solid-state image pickup device having relatively high-sensitive photoelectric conversion elements (hereinafter also referred to as “high-sensitive pixels”) and relatively low-sensitive photoelectric conversion elements (hereinafter also referred to as “low-sensitive pixels”) has been proposed in order to obtain a wide dynamic range image (see Japanese Patent Laid-Open No. 2000-69491, Japanese Patent Laid-Open No. 2000-316163 and Japanese Patent Laid-Open No. 2001-238126).
In an image pickup device described in Japanese Patent Laid-Open No. 2000-69491, color pixel groups each composed of four or two pixel units having color filters equal in color component but different in light transmittance are arranged in the form of a lattice. When the image pickup device is used, signals output from the four or two pixels in each color pixel group can be synthesized to thereby obtain a photograph image signal of a wide dynamic range.
In an image pickup device described in Japanese Patent Laid-Open No. 2000-316163, unit blocks different in sensitivity are arranged in such a cyclic color coding arrangement manner that high-sensitive blocks and low-sensitive blocks are arranged in the form of a checkered pattern. When the image pickup device is used, signals output from pixels in the high-sensitive blocks and signals output from pixels in the low-sensitive blocks can be selectively added up to thereby obtain a photograph image signal of a wide dynamic range.
In an image pickup device described in Japanese Patent Laid-Open No. 2001-238126, high-sensitive regions and low-sensitive regions are arranged alternately at intervals of two vertical lines. An image based on an image signal read from the image pickup device is formed in such a manner that high-sensitive images output from the high-sensitive regions and low-sensitive images output from the low-sensitive regions are generated separately according to the lines. After an interpolating process is applied to each region group to enlarge the image, the two region groups can be synthesized in a predetermined mixture ratio to thereby obtain a photograph image signal of a wide dynamic range.